1. Field of the Invention
The present invention relates to the separation of different density liquid components from the liquid mixture within a hydrocyclone and, more particularly, to a method and related apparatus for controlling the separation efficiency of a hydrocyclone.
2. Setting of the Invention
The utilization of hydrocyclones to separate the liquid components of a liquid mixture in relation to their densities is well known to those skilled in the art. Such hydrocyclones have been utilized in the oil production industry to separate water produced from the crude oil, because the crude oil must be essentially free of water before it can be sold or transported within pipelines. Also, the produced waste water is discharged into streams, holding ponds or into the ocean from an offshore platform. This waste water can include only a very minimal amount of oil because of environmental concerns.
To be able to remove the oil from the water is extremely difficult because the density difference between these two components is small. Typical oil/water separation hydrocyclones have a very small (such as about 1 MM) opening for the oil rich slurry to flow out to reduce the amount of water discharged with the oil. However, in the production of crude oil, it has been found that these small diameter openings may become clogged, whereupon no oil is separated and oil is discharged with the water. There is a need for an efficient oil and water separator that can be provided with mechanisms for minimizing the clogging of the small oil outlets.
Various types of hydrocyclones have been developed which include gas or liquid injection. Examples are disclosed in U.S. Pat. Nos. 3,489,680 and 4,399,027. Within these hydrocyclones, a gas or a liquid is introduced into plenum wherefrom the gas or liquid is introduced into the interior of the hydrocyclone to aid in the separation or "flotation" of the lighter density components. Nowhere is there disclosed or suggested within these patents of a system or a method of controlling the quantity of air or liquid being introduced in relation to the amount of oil found within the feed stream to minimize the discharge of water with oil when there is not much oil present and to maximize oil removal when large amounts of oil are fed to the device. At the same time, this continuous flow of air increases the necessary oil discharge diameter.
Various systems have been developed for determining the quantity of oil that is discharged with the produced water and then varying the backpressure within a hydrocyclone to minimize the quantity of oil. One such system is disclosed in U.S. Pat. No. 4,622,150 wherein an oil-in-water sensor is provided on the underflow of a hydrocyclone. A control signal from the sensor causes a valve on the overflow of the hydrocyclone to regulate the backflow within the hydrocyclone and thus control the quantity of oil that is discharged with the water. There is no disclosure or suggestion within U.S. Pat. No. 4,622,150 of varying a quantity of gas or liquid introduced into a sparged hydrocyclone, or of not restricting the overflow to control the quantity of oil discharged with water.